I would go with Jeorgen's suggestion and share everything through a database if that is possible, but just to throw this out there, you might also take a look at XML-RPC or its big brother, SOAP. Implementations of <a href='XML-RPC and SOAP exist for both perl and PHP. The SOAP::Lite module is excellent and there is a good tutorial on its use at www.perl.com. There is an implementation of SOAP for PHP as well, but I don't have the link handy.

Update:

The PHP SOAP implementation is a bit of a pain to find, so here's a link.

----
Coyote